Coal and other solid carbonaceous material can be effectively liquefied to form oil by contact with a suitable oil base solvent such as the recycled liquefaction product. Hydrogen is added as the coal dissolves to stabilize the product in liquid form. The use of a catalyst permits carrying out the process at lower temperatures and pressure than that of earlier liquefaction attempts.
It has long been appreciated that a good dispersion of the catalysts is an important factor in effective liquefaction. This invention relates to an improved method of catalyst distribution or dispersion within solid carbonaceous material. It also provides a more stable and convenient catalyst suspension.
The effective distribution of minute amounts of liquefaction catalyst throughout a powdered solid has been difficult and cumbersome. Where aqueous solution are used, large amounts of carbonaceous materials must subsequently be dried at large energy expense to remove the impregnating solution.
Therefore, in view of the above, it is an object of the present invention to provide an improved method of dispersing a liquefaction catalyst in a solid carbonaceous material.
It is a further object to provide a method of catalyst dispersion which results in good catalyst stability.
It is a further object to provide a suspension of liquefaction catalyst within water-immiscible oil that exhibits stable dispersion and good storage life.
In accordance with the present invention, a method of catalyst dispersion into a solid carbonaceous material for its liquefaction is provided. The method includes forming a solid suspension of microcapsules in carbonaceous liquid. The microcapsules have thermolabile, polymeric shells containing liquefaction catalysts. The solid carbonaceous material is contacted with the suspension at a decomposition temperature that is sufficient to destroy the microcapsule shells and provide intimate contact between the finely divided catalyst and the solid carbonaceous material.
In one other aspect of the invention, the suspension of microcapsules is formed by dissolving catalytic metal salt in an aqueous solution and blending the aqueous solution into a carbonaceous oil to form an emulsion of minute catalyst-containing droplets dispersed throughout the oil. The emulsion is converted to a solid suspension in oil by microencapsulating the minute droplets in individual capsules of polymeric thermolabile material.
In more specific aspects, the microcapsules are in a size range of about 1-20 micrometers and form a solution of about 20% solid suspension in oil with about 2.times.10.sup.9 microcapsules per cubic centimeter of suspension.
In other more specific aspects of the invention, the solid suspension is formed at a first concentration of suspended solids for storage and subsequently diluted with additional carbonaceous oil to a second but lower concentration of suspended solids for contacting and liquefaction of the carbonaceous material.
In yet other aspects of the invention, the liquefaction catalyst is a water-soluble, metal salt selected from ammonium heptamolybdate, ferrous sulfate, nickelous chloride and stannous chloride. An important catalyst is ammonium heptamolybdate.
In still other aspects of the invention, the carbonaceous liquid is a generally water immiscible oil produced at least in part by the dissolution of solid carbonaceous material of the type into which the liquefaction catalyst is distributed. Where coal is employed as the solid carbonaceous material to be recycled, coal-derived liquid provides a suitable water immiscible oil for suspension of the microcapsules containing the catalyst.
In still other aspects of the invention, the suspension of microcapsules is heated to a sufficient decomposition temperature to destroy the microcapsule shells and provide a suspension of catalytic metal crystallites throughout the oil in intimate contact with the solid carbonaceous material.
In one other manner, finely divided liquefaction catalyst can be distributed into solid carbonaceous material by dissolving a catalytic metal compound in an aqueous solution and blending the aqueous solution into a carbonaceous oil to form an emulsion. The emulsion is converted to a solid suspension in carbonaceous oil by encapsulating the minute aqueous droplets to form a fine dispersion of microcapsules. The solid suspension is heated to a sufficient decomposition temperature to destroy the microcapsules and convert the emulsion droplets to fine crystallites of catalytic material suspended in oil. On contacting the solid carbonaceous material with the suspension of catalytic crystallites, the catalyst infuses throughout the carbonaceous solids. Where ammonium heptamolybdate is selected for dissolution in aqueous solution to form the minute droplets of emulsion and oil, the solid suspension of crystallites will include molybdenum trioxide. Temperatures of about 400.degree.-500.degree. C. decompose the microcapsules and initiate liquefaction of the solid carbonaceous material.
The invention also contemplates a suspension of finely divided liquefaction catalyst in oil for the liquefaction of solid carbonaceous material. The suspension includes a water-immiscible oil, a multiplicity of microcapsules suspended throughout the oil, which microcapsules include a thin shell of thermolabile polymer containing fine droplets of catalyst in aqueous solution. In one such suspension, microcapsules are about 1-20 micron size forming about a 20% by weight solid suspension in the oil and contain fine droplets of dissolved ammonium heptamolybdate in aqueous solution.